Interpretive Summary: Insect pests in pear and apple orchards of the Pacific northwest are much less damaging during the growing season if they can be controlled successfully very early in spring. At that time of year, however, biological control in orchards is highly variable and may not provide the necessary control. Reasons for this are unknown. More information about the overwintering biology of natural enemies may assist in understanding early season biological control in orchards. Artificial shelters were placed in pear and apple orchards in late summer to provide overwintering sites for predators. A variety of natural enemies were found to use these shelters, including lacewings, ladybugs, predatory mites, spiders, and hoverflies, suggesting that many natural enemies do overwinter in orchards. By collecting shelters at regular intervals between late summer and early winter, we showed that many of these predators did not enter overwintering quarters until well into autumn. These results suggest that post-harvest applications of insecticides, as made by some growers to control pests, would also hit many predatory species, possibly affecting biological control the following spring.

Technical Abstract:
Overwintering shelters composed of cardboard bands were placed on pear and apple trees to monitor overwintering by predatory arthropods. More than 8,000 predatory arthropods were collected from bands placed in pear orchards. The Araneae were particularly diverse, including more than 3,000 spiders representing 9 families. Less abundant were Heteroptera, including a mirid and three species of Anthocoridae. Coleoptera included Coccinellidae, Staphylinidae and Carabidae. Bands that were collected at weekly intervals to monitor phenology provided more than 15,000 predatory arthropods, dominated numerically by spiders, Dermaptera, lacewings, and predatory mites. Brown lacewings began appearing in bands in late October, coinciding with leaf fall in orchards. Green lacewings, conversely, were most abundant in bands in September, well before leaf fall. Predatory mites began to appear in bands in late September before onset of leaf fall. Patterns for predatory Heteroptera were less clear, but results showed that Deraeocoris brevis and Orius tristicolor were active in the orchards well into the period of leaf fall.